Territorial Behaviour in Barnacle Settlement

Abstract

ABSTRACT An analysis of the natural pattern of settlement of barnacles, whether arranged along a groove or over a plane area, shows that later settlers tend to maintain a distance of about 2 mm. from earlier ones. This phenomenon in a sedentary form is analogous to territorial behaviour in active species. A method is described which gives average values for population density as a function of the distance from any reference individual. It is found that the reference individual lies in a trough of very low population density, and that the latter rises sharply a short distance away. The distance from the reference individual, at which the population density reaches the average value for the whole population, is defined as the territorial separation. The territorial separation is reduced, but not entirely eliminated, as the population density rises. The value of territorial separation is a little greater than the sum of the radius of the previously settled spat and the length of the cyprid, and is slightly smaller in species with smaller cyprids and spat. Cyprids settle at the periphery of the base of detached specimens rather than at the centre. Though strongly attracted to pits in the surface, cyprids continue to behave territorially within a pit, and avoid pits containing previously settled individuals. They settle readily in pits with only the bases of detached individuals present. Observations on settling cyprids show that after encountering settled barnacles they tend to remain and explore the surface. If they continue to encounter settled individuals at the time they are about to settle, the period of final searching is prolonged until they find a suitably vacant area. Territorial behaviour is probably an adaptation allowing the recently metamorphosed cyprid time to establish itself before it touches the growing edge of another barnacle.